Such lenses may generally be made out of bits of good plate or sheet glass, and are of constant use in the physical laboratory.
The gathering for sheet glass is done much as was that for the smaller pieces.
American sheet glass is made in two thicknesses—single and double strength—and in four qualities.
The sheet glass which is obscured by a system of wrinkles on its surface is, however, sometimes known as "maze-glass."
Differently arranged furnaces are used for bottles from those employed for crown and sheet glass.
With these words he held out a small bit of sheet glass about two inches square.